Re: [PATCH for 4.6 13/13] xen/iommu: smmu: Add Xen specific code to be able to use the driver

[Julien Grall <julien.grall@linaro.org>]

On 19/02/2015 02:55, Manish wrote:
>
> On 18/02/15 11:52 pm, Julien Grall wrote:
>>
>>
>> On 18/02/2015 17:30, Jaggi, Manish wrote:
>>> [manish] There are general comments on the data structures
>>> (a) I don't see a use case where for same domain (VM) there would be
>>> different context banks , so linked list may not be required.
>>
>> I guess you mean the list in arm_smmu_xen_domain? All the devices
>> pass-through to a domain may not be protected by the same SMMU.
>> Therefore the context banks are different.
> you are right. For each smmu the context bank instance for a xen domain
> is duplicated with just a change in context bank id. I was thinking can
> it be minimized.
>>
>> Also, for now a context is allocated per-device. It should be rework
>> to share the context between multiple device protected by the same
>> SMMU and pass-through to the same domain.
> Yes, this is exactly I an doing at my end.
>>
>>> (b) Also iommu group may not be relevant for the same reason.
>>> I am curious to find the use cases.
>>
>> The iommu_group is used to store the configuration of the device
>> protected by an SMMU (i.e the stream ids associated to this domain).
>>
>> I'm a bit surprised that you think they are not useful...
> How do we create an iommu_group in xen ? AFAIK an iommu group is a vfio
> group in linux which is assigned to a a VM.
> lkvm run -m 512 -k home/Image ...  --vfio-groups=48, 51

  > For Xen There are 2 ways of attaching devices using xl pci-attach or in
> domU cfg file. Should they create different iommu_groups ?

Why are you talking about VFIO? The iommu_group is created by the SMMU 
when a new device is added (see arm_smmu_device). At the time we are 
speaking, Linux and Xen use one iommu group per-device. No matters what 
VFIO does.

Even though we have two ways to attach PCI on the toolstack, both are 
using the same hypercall at the end.

Regards,

-- 
Julien Grall